Protective effects of estradiol on ethanol-induced bone loss involve inhibition of reactive oxygen species generation in osteoblasts and downstream activation of the extracellular signal-regulated kinase/signal transducer and activator of transcription 3/receptor activator of nuclear factor-kappaB ligand signaling cascade

Subchondral osteoclasts and osteoarthritis: new insights and potential therapeutic avenues

Osteoarthritis (OA) is the most common joint disease, and good therapeutic results are often difficult to obtain due to its complex pathogenesis and diverse causative factors. After decades of research and exploration of OA, it has been progressively found that subchondral bone is essential for its pathogenesis, and pathological changes in subchondral bone can be observed even before cartilage lesions develop. Osteoclasts, the main cells regulating bone resorption, play a crucial role in the pathogenesis of subchondral bone. Subchondral osteoclasts regulate the homeostasis of subchondral bone through the secretion of degradative enzymes, immunomodulation, and cell signaling pathways. In OA, osteoclasts are overactivated by autophagy, ncRNAs, and Rankl/Rank/OPG signaling pathways. Excessive bone resorption disrupts the balance of bone remodeling, leading to increased subchondral bone loss, decreased bone mineral density and consequent structural damage to articular cartilage and joint pain. With increased understanding of bone biology and targeted therapies, researchers have found that the activity and function of subchondral osteoclasts are affected by multiple pathways. In this review, we summarize the roles and mechanisms of subchondral osteoclasts in OA, enumerate the latest advances in subchondral osteoclast-targeted therapy for OA, and look forward to the future trends of subchondral osteoclast-targeted therapies in clinical applications to fill the gaps in the current knowledge of OA treatment and to develop new therapeutic strategies.

Nanozymes With Osteochondral Regenerative Effects: An Overview of Mechanisms and Recent Applications

With the discovery of the intrinsic enzyme-like activity of metal oxides, nanozymes garner significant attention due to their superior characteristics, such as low cost, high stability, multi-enzyme activity, and facile preparation. Notably, in the field of biomedicine, nanozymes primarily focus on disease detection, antibacterial properties, antitumor effects, and treatment of inflammatory conditions. However, the potential for application in regenerative medicine, which primarily addresses wound healing, nerve defect repair, bone regeneration, and cardiovascular disease treatment, is garnering interest as well. This review introduces nanozymes as an innovative strategy within the realm of bone regenerative medicine. The primary focus of this approach lies in the facilitation of osteochondral regeneration through the modulation of the pathological microenvironment. The catalytic mechanisms of four types of representative nanozymes are first discussed. The pathological microenvironment inhibiting osteochondral regeneration, followed by summarizing the therapy mechanism of nanozymes to osteochondral regeneration barriers is introduced. Further, the therapeutic potential of nanozymes for bone diseases is included. To improve the therapeutic efficiency of nanozymes and facilitate their clinical translation, future potential applications in osteochondral diseases are also discussed and some significant challenges addressed.

Impact of Alcohol on Bone Health in People Living With HIV: Integrating Clinical Data From Serum Bone Markers With Morphometric Analysis in a Non-Human Primate Model

People living with HIV (PLWH) represent a vulnerable population to adverse musculoskeletal outcomes due to HIV infection, antiretroviral therapy (ART), and at-risk alcohol use. Developing measures to prevent skeletal degeneration in this group requires a grasp of the relationship between alcohol use and low bone mass in both the PLWH population and its constituents as defined by sex, age, and race. We examined the association of alcohol use with serum biochemical markers of bone health in a diverse cohort of PLWH enrolled in the New Orleans Alcohol Use in HIV (NOAH) study. To explore the effects of alcohol on bone in the context of HIV and ART and the role of estrogen, we conducted a parallel, translational study using simian immunodeficiency virus (SIV)+/ART+ female rhesus macaques divided into four groups: vehicle (Veh)/Sham; chronic binge alcohol (CBA)/Sham; Veh/ovariectomy (OVX); and CBA/OVX. Clinical data showed that both osteocalcin (Ocn) and procollagen type I N-propeptide (PINP) levels were inversely associated with multiple measures of alcohol consumption. Age (>50 years) significantly increased susceptibility to alcohol-associated suppression of bone formation in both female and male PLWH, with postmenopausal status appearing as an additional risk factor in females. Serum sclerostin (Scl) levels correlated positively with measures of alcohol use and negatively with Ocn. Micro-CT analysis of the macaque tibias revealed that although both CBA and OVX independently decreased trabecular number and bone mineral density, only OVX decreased trabecular bone volume fraction and impacted cortical geometry. The clinical data implicate circulating Scl in the pathogenesis of alcohol-induced osteopenia and suggest that bone morphology can be significantly altered in the absence of net change in osteoblast function as measured by serum markers. Inclusion of sophisticated tools to evaluate skeletal strength in clinical populations will be essential to understand the impact of alcohol-induced changes in bone microarchitecture. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Nox4 promotes osteoblast differentiation through TGF-beta signal pathway

NADPH oxidase 4 (Nox4) is the main source of reactive oxygen species, which promote osteoclast formation and lead to bone loss, thereby causing osteoporosis. However, the role of Nox4 in osteoblasts during early development remains unclear. We used zebrafish to study the effect of Nox4 deletion on bone mineralization in early development. nox4-/- zebrafish showed decreased bone mineralization during early development and significantly reduced numbers of osteoblasts, osteoclasts, and chondrocytes. Transcriptome sequencing showed that the TGF-β signaling pathway was significantly disrupted in nox4-/- zebrafish. Inhibiting TGF-β signaling rescued the abnormal bone development caused by nox4 deletion and increased the number of osteoblasts. We used Saos-2 human osteosarcoma cells to confirm our results, which clarified the role of Nox4 in human osteoblasts. Our results demonstrate the mechanism of reduced bone mineralization in early development and provide a basis for the clinical treatment of osteoporosis.

Nox4 expression in osteo-progenitors controls bone development in mice during early life

Tightly regulated and cell-specific NADPH-oxidases (Nox) represent one of the major sources of reactive oxygen species (ROS) signaling molecules that are involved in tissue development and stem cell self-renewal. We have characterized the role of Nox4 in osteo-progenitors during postnatal bone development. Nox4 expression in bone and ROS generation were increased during early osteoblast differentiation and bone development. Stromal osteoblastic cell self-renewal, proliferation and ROS production were significantly lower in samples from whole-body Nox4 knockout mice (Nox4^-/-) and conditional knockout (CKO) mice with depletion of Nox4 in the limb bud mesenchyme compared with those from control mice (Nox4^fl/fl), but they were reversed after 9 passages. In both sexes, bone volume, trabecular number and bone mineral density were significantly lower in 3-week old CKO and Nox4^-/- mice compared with Nox4^fl/fl controls. This was reflected in serum levels of bone formation markers alkaline phosphatase (ALP) and procollagen 1 intact N-terminal propeptide (P1NP). However, under-developed bone formation in 3-week old CKO and Nox4^-/- mice quickly caught up to levels of control mice by 6-week of age, remained no different at 13-week of age, and was reversed in 32-week old male mice. Osteoclastogenesis showed no differences among groups, however, CTX1 reflecting osteoclast activity was significantly higher in 3-week old male CKO and Nox4^-/- mice compared with control mice, and significantly lower in 32-week old Nox4^-/- mice compared with control mice. These data suggest that Nox4 expression and ROS signaling in bone and osteoblastic cells coordinately play an important role in osteoblast differentiation, proliferation and maturation.

Episodic alcohol exposure attenuates mesenchymal stem cell chondrogenic differentiation during bone fracture callus formation

BACKGROUND

During bone fracture repair, mesenchymal stem cells (MSC) differentiate into chondrocytes and osteoblasts to form a fracture callus. Our laboratory previously reported that alcohol-exposed rodents with a surgically created tibia fracture display deficient fracture callus formation and diminished signs of endochondral ossification characterized by the absence of chondrocytes and mature hypertrophic chondrocytes, suggesting that alcohol may inhibit MSC differentiation. These findings led to our hypothesis that alcohol exposure inhibits mesenchymal stem cell chondrogenic differentiation within the developing fracture callus.

METHODS

In the present study, we utilized a lineage-tracing approach to determine which stage(s) of chondrogenic differentiation are affected by alcohol exposure. We utilized lineage-specific reporter mice to determine the effects of alcohol on MSC and early and late chondrogenic cell frequencies within the fracture callus. In addition, serially sectioned slides were stained immunofluorescently and immunohistochemically and quantified to determine the effect of alcohol on cell proliferation and apoptosis, respectively, within the fracture callus of alcohol-administered rodents.

RESULTS

Alcohol-administered rodents had a reduced fracture callus area at 4, 6, and 9 days postfracture. Alcohol had no effect on apoptosis in the fracture callus at any of the examined timepoints. Alcohol-administered rodents had significantly fewer proliferative cells in the fracture callus at 9 days postfracture, but no effect on cell proliferation was observed at earlier fracture callus timepoints. Alcohol-administered rodents had reduced Collagen2a1- and Collagen10a1-expressing cells in the developing fracture callus, suggesting that alcohol inhibits both early chondrogenic differentiation and later chondrocyte maturation during fracture callus development.

CONCLUSION

The data suggest that alcohol could affect normal fracture healing through the mitigation of MSC chondrogenic differentiation at the callus site.

Autophagy in Bone Remodeling: A Regulator of Oxidative Stress

Bone homeostasis involves bone formation and bone resorption, which are processes that maintain skeletal health. Oxidative stress is an independent risk factor, causing the dysfunction of bone homeostasis including osteoblast-induced osteogenesis and osteoclast-induced osteoclastogenesis, thereby leading to bone-related diseases, especially osteoporosis. Autophagy is the main cellular stress response system for the limination of damaged organelles and proteins, and it plays a critical role in the differentiation, apoptosis, and survival of bone cells, including bone marrow stem cells (BMSCs), osteoblasts, osteoclasts, and osteocytes. High evels of reactive oxygen species (ROS) induced by oxidative stress induce autophagy to protect against cell damage or even apoptosis. Additionally, pathways such as ROS/FOXO3, ROS/AMPK, ROS/Akt/mTOR, and ROS/JNK/c-Jun are involved in the regulation of oxidative stress-induced autophagy in bone cells, including osteoblasts, osteocytes and osteoclasts. This review discusses how autophagy regulates bone formation and bone resorption following oxidative stress and summarizes the potential protective mechanisms exerted by autophagy, thereby providing new insights regarding bone remodeling and potential therapeutic targets for osteoporosis.

Adverse Effects of Oxidative Stress on Bone and Vasculature in Corticosteroid-Associated Osteonecrosis: Potential Role of Nuclear Factor Erythroid 2-Related Factor 2 in Cytoprotection

Significance: Osteonecrosis (ON) is characterized by bone tissue death due to disturbance of the nutrient artery. The detailed process leading to the necrotic changes has not been fully elucidated. Clinically, high-dose corticosteroid therapy is one of the main culprits behind osteonecrosis of the femoral head (ONFH). Recent Advances: Numerous studies have proposed that such ischemia concerns various intravascular mechanisms. Of all reported risk factors, the involvement of oxidative stress in the irreversible damage suffered by bone-related and vascular endothelial cells during ischemia simply cannot be overlooked. Several articles also have sought to elucidate oxidative stress in relation to ON using animal models or in vitro cell cultures. Critical Issues: However, as far as we know, antioxidant monotherapy has still not succeeded in preventing ONFH in humans. To provide this desideratum, we herein summarize the current knowledge about the influence of oxidative stress on ON, together with data about the preventive effects of administering antioxidants in corticosteroid-induced ON animal models. Moreover, oxidative stress is counteracted by nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent cytoprotective network through regulating antioxidant expressions. Therefore, we also describe Nrf2 regulation and highlight its role in the pathology of ON. Future Directions: This is a review of all available literature to date aimed at developing a deeper understanding of the pathological mechanism behind ON from the perspective of oxidative stress. It may be hoped that this synthesis will spark the development of a prophylactic strategy to benefit corticosteroid-associated ONFH patients. Antioxid. Redox Signal. 35, 357-376.

The Impact of Sedentary Lifestyle, High-fat Diet, Tobacco Smoke, and Alcohol Intake on the Hematopoietic Stem Cell Niches

Hematopoietic stem and progenitor cells maintain hematopoiesis throughout life by generating all major blood cell lineages through the process of self-renewal and differentiation. In adult mammals, hematopoietic stem cells (HSCs) primarily reside in the bone marrow (BM) at special microenvironments called “niches.” Niches are thought to extrinsically orchestrate the HSC fate including their quiescence and proliferation. Insight into the HSC niches mainly comes from studies in mice using surface marker identification and imaging to visualize HSC localization and association with niche cells. The advantage of mouse models is the possibility to study the 3-dimensional BM architecture and cell interactions in an intact traceable system. However, this may not be directly translational to human BM. Sedentary lifestyle, unhealthy diet, excessive alcohol intake, and smoking are all known risk factors for various diseases including hematological disorders and cancer, but how do lifestyle factors impact hematopoiesis and the associated niches? Here, we review current knowledge about the HSC niches and how unhealthy lifestyle may affect it. In addition, we summarize epidemiological data concerning the influence of lifestyle factors on hematological disorders and malignancies.

Systems pharmacology dissection of action mechanisms for herbs in osteoporosis treatment

Objective

Osteoporosis has become the biggest cause of non-fatal health issue. Currently, the limitations of traditional anti-osteoporosis drugs such as long-term ill-effects and drug resistance, have raised concerns toward complementary and alternative therapies, particularly herbal medicines and their natural active compounds. Thus, this study aimed to provide an integrative analysis of active chemicals, drug targets and interacting pathways of the herbs for osteoporosis treatment.

Methods

Here, we introduced a systematic pharmacology model, combining the absorption, distribution, metabolism, and excretion (ADME) screening model, drug targeting and network pharmacology, to probe into the therapeutic mechanisms of herbs in osteoporosis.

Results

We obtained 86 natural compounds with favorable pharmacokinetic profiles and their 58 targets from seven osteoporosis-related herbs. Network analysis revealed that they probably synergistically work through multiple mechanisms, such as suppressing inflammatory response, maintaining bone metabolism or improving organism immunity, to benefit patients with osteoporosis. Furthermore, experimental results showed that all the five compounds (calycosin, asperosaponin VI, hederagenin, betulinic acid and luteolin) enhanced osteoblast proliferation and differentiation in vitro, which corroborated the validity of this system pharmacology approach. Notably, gentisin and aureusidin among the identified compounds were first predicted to be associated with osteoporosis.

Conclusion

Herbs and their natural compounds, being characterized as the classical combination therapies, might be engaged in multiple mechanisms to coordinately improve the osteoporosis symptoms. This work may contribute to offer novel strategies and clues for the therapy and drug discovery of osteoporosis and other complex diseases.

Potential mechanisms linking psychological stress to bone health

Chronic psychological stress affects many body systems, including the skeleton, through various mechanisms. This review aims to provide an overview of the factors mediating the relationship between psychological stress and bone health. These factors can be divided into physiological and behavioural changes induced by psychological stress. The physiological factors involve endocrinological changes, such as increased glucocorticoids, prolactin, leptin and parathyroid hormone levels and reduced gonadal hormones. Low-grade inflammation and hyperactivation of the sympathetic nervous system during psychological stress are also physiological changes detrimental to bone health. The behavioural changes during mental stress, such as altered dietary pattern, cigarette smoking, alcoholism and physical inactivity, also threaten the skeletal system. Psychological stress may be partly responsible for epigenetic regulation of skeletal development. It may also mediate the relationship between socioeconomic status and bone health. However, more direct evidence is required to prove these hypotheses. In conclusion, chronic psychological stress should be recognised as a risk factor of osteoporosis and stress-coping methods should be incorporated as part of the comprehensive osteoporosis-preventing strategy.

Male predisposition to severe COVID-19: Review of evidence and potential therapeutic prospects

The severe form of COVID-19 has significant sex disparities, with high fatalities commonly reported among males than females. The incidence of COVID-19 has also been higher in males compared with their female counterparts. This trend could be attributed to a better responsive and robust immune system in females. Cytokine storm is one of the pathophysiological features of severe COVID-19, and it occurs as a result of over-activation of immune cells leading to severe inflammation and tissue damage. Nevertheless, it is well modulated in females compared to their male counterparts. Severe inflammation in males is reported to facilitate progression of mild to severe COVID-19. The sex hormones, estrogens and androgens which exist in varying functional levels respectively in females and males are cited as the underlying cause for the differential immune response to COVID-19. Evidence abounds that estrogen modulate the immune system to protect females from severe inflammation and for that matter severe COVID-19. On the contrary, androgen has been implicated in over-activation of immune cells, cytokine storm and the attendant severe inflammation, which perhaps predispose males to severe COVID-19. In this review efforts are made to expand understanding and explain the possible roles of the immune system, the sex hormones and the angiotensin-converting enzyme (ACE) systems in male bias to severe COVID-19. Also, this review explores possible therapeutic avenues including androgen deprivation therapy (ADT), estrogen-based therapy, and ACE inhibitors for consideration in the fight against COVID-19.

NADPH oxidases in bone and cartilage homeostasis and disease: A promising therapeutic target

Reactive oxygen species (ROS) generated by the NADPH oxidase (Nox) enzymes are important short-range signaling molecules. They have been extensively studied in the physiology and pathophysiology of the cardiovascular system, where they have important roles in vascular inflammation, angiogenesis, hypertension, cardiac injury, stroke, and aging. Increasing evidence demonstrates that ROS and Nox enzymes also affect bone homeostasis and osteoporosis, and more recent studies implicate ROS and Nox enzymes in both inflammatory arthritis and osteoarthritis. Mechanistically, this connection may be through the effects of ROS on signal transduction. ROS affect both transforming growth factor-β/Smad signaling, interleukin-1β/nuclear factor-kappa B signaling, and the resulting changes in matrix metalloproteinase expression. The purpose of this review is to describe the role of Nox enzymes in the physiology and pathobiology of bone and joints and to highlight the potential of therapeutically targeting the Nox enzymes.

Impact of Alcohol on Bone Health, Homeostasis and Fracture repair

Purpose of review

Alcohol use continues to rise globally. We review the current literature on the effect of alcohol on bone health, homeostasis and fracture repair to highlight what has been learned in people and animal models of alcohol consumption.

Recent findings

Recently, forkhead box O (FoxO) has been found to be upregulated and activated in mesenchymal stem cells (MSC) exposed to alcohol. FoxO has also been found to modulate Wnt/β-catenin signaling, which is necessary for MSC differentiation. Recent evidence suggests alcohol activates FoxO signaling, which may be dysregulating Wnt/β-catenin signaling in MSCs cultured in alcohol.

Summary

This review highlights the negative health effects learned from people and chronic and episodic binge alcohol consumption animal models. Studies using chronic alcohol exposure or alcohol exposure then bone fracture repair model have explored several different cellular and molecular signaling pathways important for bone homeostasis and fracture repair, and offer potential for future experiments to explore additional signaling pathways that may be dysregulated by alcohol exposure.

Chronic Ethanol Feeding in Mice Decreases Expression of Genes for Major Structural Bone Proteins in a Nox4-Independent Manner

Bone loss in response to alcohol intake has previously been hypothesized to be mediated by excessive production of reactive oxygen species via NADPH oxidase (Nox) enzymes. Nox4 is one of several Nox enzymes expressed in bone. We investigated the role of Nox4 in the chondro-osteoblastic lineage of the long bones in mice during normal chow feeding and during chronic ethanol feeding for 90 days. We generated mice with a genotype (PrxCre +/- Nox4 fl/fl) allowing conditional knockout of Nox4 in the limb bud mesenchyme. Adult mice had 95% knockdown of Nox4 expression in the femoral shafts. For mice on regular chow, only whole-body Nox4 knockout mice had clearly increased cortical thickness and bone mineral density in the tibiae. When chronically fed a liquid diet with and without ethanol, conditional Nox4 knockout mice had slightly reduced dimensions of the cortical and trabecular regions of the tibiae (P < 0.1). The ethanol diet caused a significant reduction in cortical bone area and cortical thickness relative to a control diet without ethanol (P < 0.05). The ethanol diet further reduced gene expression of Frizzled related protein (Frzb), myosin heavy chain 3, and several genes encoding collagen and other major structural bone proteins (P < 0.05), whereas the Nox4 genotype had no effects on these genes. In conclusion, Nox4 expression from both mesenchymal and nonmesenchymal cell lineages appears to exert subtle effects on bone. However, chronic ethanol feeding reduces cortical bone mass and cortical gene expression of major structural bone proteins in a Nox4-independent manner. SIGNIFICANCE STATEMENT: Excessive alcohol intake contributes to osteopenia and osteoporosis, with oxidative stress caused by the activity of NADPH oxidases hypothesized to be a mediator. We tested the role of NADPH oxidase (Nox) 4 in osteoblast precursors in the long bones of mice with a conditional Nox4 knockout model. We found that Nox4 exerted effects independent of alcohol intake, and ethanol effects on bone were Nox4-independent.

RANKL/RANK/OPG Pathway: A Mechanism Involved in Exercise-Induced Bone Remodeling

Bones as an alive organ consist of about 70% mineral and 30% organic component. About 200 million people are suffering from osteopenia and osteoporosis around the world. There are multiple ways of protecting bone from endogenous and exogenous risk factors. Planned physical activity is another useful way for protecting bone health. It has been investigated that arranged exercise would effectively regulate bone metabolism. Until now, a number of systems have discovered how exercise could help bone health. Previous studies reported different mechanisms of the effect of exercise on bone health by modulation of bone remodeling. However, the regulation of RANKL/RANK/OPG pathway in exercise and physical performance as one of the most important remodeling systems is not considered comprehensive in previous evidence. Therefore, the aim of this review is to clarify exercise influence on bone modeling and remodeling, with a concentration on its role in regulating RANKL/RANK/OPG pathway.

Disulfiram suppressed ethanol promoted RANKL-induced osteoclastogenesis in vitro and ethanol-induced osteoporosis in vivo via ALDH1A1-NFATc1 axis

Excessive alcohol consumption is positively related to osteoporosis, and its treatment strategies are poorly developed. Disulfiram inhibits receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis; however, whether it can be used for ethanol-induced osteoclastogenesis and its underlying mechanism are still unclear. In this study, we demonstrated that ethanol promoted RANKL-induced osteoclast formation and bone resorption, whereas, disulfiram suppressed ethanol-induced osteoclastogenesis by abrogating the expression of nuclear factor of activated T cell c1 (NFATc1) in vitro. Further analysis revealed that aldehyde dehydrogenase 1A1 (ALDH1A1) is important for the expression of NFATc1, the master regulator of osteoclast differentiation. Furthermore, we showed that disulfiram protected ethanol-induced osteoporosis in vivo. Overall, our study provides promising evidence that disulfiram can be used as a treatment strategy for alcohol-related osteoporosis via the ALDH1A1T–NFATc1 axis.

Serum levels of carotenoids in patients with osteonecrosis of the femoral head are lower than in healthy, community-living people

PURPOSE

Oxidative stress is closely associated with the pathogenesis of nontraumatic osteonecrosis of the femoral head (ONFH). This study aimed to determine whether the serum levels of antioxidant nutrients were decreased in patients with ONFH.

METHODS

We analyzed the serum levels of antioxidant nutrients in 39 patients with ONFH (ONFH group) and 78 age- and gender-matched healthy people (control group) who voluntarily participated in the Yakumo study, which is a comprehensive health examination program. We measured and compared the serum levels of α-tocopherol (vitamin E) and total carotenoids, including zeaxanthin/lutein, β-cryptoxanthin, lycopene, α-carotene, and β-carotene, in the ONFH and control groups using high-performance liquid chromatography.

RESULTS

The mean serum levels of total carotenoids were significantly lower in the ONFH group than in the control group (2.36 ± 1.26 and 3.79 ± 2.36 µmol/l, respectively, p < 0.001). However, no significant difference was found in α-tocopherol between the two groups (26.37 ± 6.90 µmol/l in the ONFH group and 26.24 ± 6.28 µmol/l in the control group, p = 0.920). Among each carotenoid, the serum levels of zeaxanthin/lutein, lycopene, and β-carotene were significantly lower in the ONFH group than in the control group ( p < 0.001).

CONCLUSIONS

The serum levels of carotenoids were lower in patients with ONFH than in healthy, community-living people. This result suggests that carotenoids may be related to the pathogenesis of ONFH.

NOX4 Deletion in Male Mice Exacerbates the Effect of Ethanol on Trabecular Bone and Osteoblastogenesis

Chronic alcohol consumption increases bone resorption and decreases bone formation. A major component of ethanol (EtOH) pathology in bone is the generation of excess reactive oxygen species (ROS). The ROS-generating NADPH oxidase-4 (NOX4) is proposed to drive much of the EtOH-induced suppression of bone formation. Here, 13-week-old male wild-type (WT) and NOX4^-/- mice were pair fed (PF) a high-fat (35%), Lieber-DeCarli liquid diet with or without EtOH at 30% of their total calories for 12 weeks. Micro-computed tomography analysis demonstrated significant decreases in trabecular bone volume/total volume (BV/TV) percentage and cortical thickness in WT, EtOH-fed mice compared with PF controls. EtOH-fed NOX4^-/- mice also displayed decreased trabecular BV/TV and trabecular number compared with PF (P < 0.05). However, NOX4^-/- mice were protected against EtOH-induced decreases in cortical thickness (P < 0.05) and decreases in collagen1 and osteocalcin mRNA expression in cortical bone (P < 0.05). In WT and NOX4^-/- vertebral bone, EtOH suppressed expression of Wnt signaling components that promote osteoblast maturation. A role for NOX4 in EtOH inhibition of osteoblast differentiation was further demonstrated by protection against EtOH inhibition of osteoblastogenesis in ex vivo bone marrow cultures from NOX4^-/-, but not p47^phox-/- mice lacking active NADPH oxidase-2. However, bone marrow cultures from NOX4^-/- mice formed fewer osteoblastic colonies compared with WT cultures (P < 0.05), suggesting a role for NOX4 in the maintenance of mesenchymal progenitor cell populations. These data suggest that NOX4 deletion is partially protective against EtOH effects on osteoblast differentiation, but may predispose bone to osteogenic impairments.

Mangiferin inhibits apoptosis and oxidative stress via BMP2/Smad-1 signaling in dexamethasone-induced MC3T3-E1 cells

Mangiferin is a xanthone glucoside, which possesses antioxidant, antiviral, antitumor and anti-inflammatory functions, and is associated with gene regulation. However, it remains unknown whether mangiferin protects osteoblasts, such as the MC3T3-E1 cell line, against glucocorticoid-induced damage. In the present study, MC3T3-E1 cells were treated with dexamethasone (Dex), which is a well-known synthetic glucocorticoid, in order to establish a glucocorticoid-induced cell injury model. After Dex and/or mangiferin treatment, cell viability, apoptosis and reactive oxygen species (ROS) production was measured by Cell Counting kit-8 (CCK-8) and flow cytometry, respectively, and the concentration of tumor necrosis factor (TNF)-α, interleukin (IL)-6 and macrophage colony-stimulating factor (M-CSF) was measured by ELISA. The expression of bone morphogenetic protein 2 (BMP2), phosphorylated-SMAD family member 1 (p-Smad-1), t-Smad-1, osterix (OSX), osteocalcin (OCN), osteoprotegerin (OPG), receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL), B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (Bax) was measured by real-time PCR and/or western blot analysis. The results indicated that pretreatment of MC3T3-E1 cells with mangiferin for 3 h prior to exposure to Dex for 48 h significantly attenuated Dex-induced injury and inflammation, as demonstrated by increased cell viability, and decreases in apoptosis, ROS generation, and the secretion of TNF-α, IL-6 and M-CSF. In addition, pretreatment with mangiferin markedly reduced Dex-induced BMP2 and p-Smad-1 downregulation, and corrected the expression of differentiation- and apoptosis-associated markers, including alkaline phosphatase, OSX, OCN, OPG, RANK, RANKL, Bcl-2 and Bax, which were altered by Dex treatment. Similar to the protective effects of mangiferin, overexpression of BMP2 suppressed not only Dex-induced cytotoxicity, but also ROS generation, and the secretion of TNF-α, IL-6 and M-CSF. In conclusion, the results of the present study are the first, to the best of our knowledge, to demonstrate that mangiferin protects MC3T3-E1 cells against Dex-induced apoptosis and oxidative stress by activating the BMP2/Smad-1 signaling pathway.

Cellular and molecular mechanisms of alcohol-induced osteopenia

Alcoholic beverages are widely consumed, resulting in a staggering economic cost in different social and cultural settings. Types of alcohol consumption vary from light occasional to heavy, binge drinking, and chronic alcohol abuse at all ages. In general, heavy alcohol consumption is widely recognized as a major epidemiological risk factor for chronic diseases and is detrimental to many organs and tissues, including bones. Indeed, recent findings demonstrate that alcohol has a dose-dependent toxic effect in promoting imbalanced bone remodeling. This imbalance eventually results in osteopenia, an established risk factor for osteoporosis. Decreased bone mass and strength are major hallmarks of osteopenia, which is predominantly attributed not only to inhibition of bone synthesis but also to increased bone resorption through direct and indirect pathways. In this review, we present knowledge to elucidate the epidemiology, potential pathogenesis, and major molecular mechanisms and cellular effects that underlie alcoholism-induced bone loss in osteopenia. Novel therapeutic targets for correcting alcohol-induced osteopenia are also reviewed, such as modulation of proinflammatory cytokines and Wnt and mTOR signaling and the application of new drugs.

Does Oxidative Stress Induced by Alcohol Consumption Affect Orthodontic Treatment Outcome?

HIGHLIGHTS Ethanol, Periodontal ligament, Extracellular matrix, Orthodontic movement. Alcohol is a legal drug present in several drinks commonly used worldwide (chemically known as ethyl alcohol or ethanol). Alcohol consumption is associated with several disease conditions, ranging from mental disorders to organic alterations. One of the most deleterious effects of ethanol metabolism is related to oxidative stress. This promotes cellular alterations associated with inflammatory processes that eventually lead to cell death or cell cycle arrest, among others. Alcohol intake leads to bone destruction and modifies the expression of interleukins, metalloproteinases and other pro-inflammatory signals involving GSKβ, Rho, and ERK pathways. Orthodontic treatment implicates mechanical forces on teeth. Interestingly, the extra- and intra-cellular responses of periodontal cells to mechanical movement show a suggestive similarity with the effects induced by ethanol metabolism on bone and other cell types. Several clinical traits such as age, presence of systemic diseases or pharmacological treatments, are taken into account when planning orthodontic treatments. However, little is known about the potential role of the oxidative conditions induced by ethanol intake as a possible setback for orthodontic treatment in adults.

Partial Protection by Dietary Antioxidants Against Ethanol-Induced Osteopenia and Changes in Bone Morphology in Female Mice

BACKGROUND

Chronic alcohol consumption leads to increased fracture risk and an elevated risk of osteoporosis by decreasing bone accrual through increasing osteoclast activity and decreasing osteoblast activity. We have shown that this mechanism involves the generation of reactive oxygen species (ROS) produced by NADPH oxidases. It was hypothesized that different dietary antioxidants, N-acetyl cysteine (NAC; 1.2 mg/kg/d), and α-tocopherol (Vit.E; 60 mg/kg/d) would be able to attenuate the NADPH oxidase-mediated ROS effects on bone due to chronic alcohol intake.

METHODS

To study the effects of these antioxidants, female mice received a Lieber-DeCarli liquid diet containing ethanol (EtOH) with or without additional antioxidant for 8 weeks.

RESULTS

Tibias displayed decreased cortical bone mineral density in both the EtOH and EtOH + antioxidant groups compared to pair-fed (PF) and PF + antioxidant groups (p < 0.05). However, there was significant protection from trabecular bone loss in mice fed either antioxidant (p < 0.05). Microcomputed tomography analysis demonstrated a significant decrease in bone volume (bone volume/tissue volume) and trabecular number (p < 0.05), along with a significant increase in trabecular separation in the EtOH compared to PF (p < 0.05). In contrast, the EtOH + NAC and EtOH + Vit.E did not statistically differ from their respective PF controls. Ex vivo histologic sections of tibias were stained for nitrotyrosine, an indicator of intracellular damage by ROS, and tibias from mice fed EtOH exhibited significantly more staining than PF controls. EtOH treatment significantly increased the number of marrow adipocytes per mm as well as mRNA expression of aP2, an adipocyte marker in bone. Only NAC was able to reduce the number of marrow adipocytes to PF levels. EtOH-fed mice exhibited reduced bone length (p < 0.05) and had a reduced number of proliferating chondrocytes within the growth plate. NAC and Vit.E prevented this (p < 0.05).

CONCLUSIONS

These data show that alcohol's pathological effects on bone extend beyond decreasing bone mass and suggest a partial protective effect of the dietary antioxidants NAC and Vit.E at these doses with regard to alcohol effects on bone turnover and bone morphology.

Alcohol-related deficient fracture healing is associated with activation of FoxO transcription factors in mice

The process of fracture healing is complex, and poor or incomplete healing remains a significant health problem. Proper fracture healing relies upon resident mesenchymal stem cell (MSC) differentiation into chondrocytes and osteoblasts, which are necessary for callus formation and ossification. Alcohol abuse is a leading contributor to poor fracture healing. Although the mechanism behind this action is unknown, excessive alcohol consumption is known to promote systemic oxidative stress. The family of FoxO transcription factors is activated by oxidative stress, and FoxO activation antagonizes Wnt signaling, which regulates mesenchymal stem cell differentiation. We hypothesize that alcohol exposure increases oxidative stress leading to deficient fracture repair by activating FoxO transcription factors within the fracture callus which disrupts chondrogenesis of mesenchymal stem cells. Our laboratory has developed an experimental model of delayed fracture union in mice using ethanol administration. We have found that ethanol administration significantly decreases external, cartilaginous callus formation, and hallmarks of endochondral ossification, and these changes are concomitant with increases in FoxO expression and markers of activation in fracture callus tissue of these mice. We were able to prevent these alcohol-induced effects with the administration of the antioxidant n-acetyl cysteine (NAC), suggesting that alcohol-induced oxidative stress produces the perturbed endochondral ossification and FoxO expression. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2106-2115, 2016.

Chronic High Dose Alcohol Induces Osteopenia via Activation of mTOR Signaling in Bone Marrow Mesenchymal Stem Cells

Chronic consumption of excessive alcohol results in reduced bone mass, impaired bone structure, and increased risk of bone fracture. However, the mechanisms underlying alcohol-induced osteoporosis are not fully understood. Here, we show that high dose chronic alcohol consumption reduces osteogenic differentiation and enhances adipogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs), leading to osteopenia in a mouse model. Mechanistically, impaired osteo/adipogenic lineage differentiation of BMMSCs is due to activation of a phosphatidylinositide 3-kinase/AKT/mammalian target of rapamycin (mTOR) signaling cascade, resulting in downregulation of runt-related transcription factor 2 and upregulation of peroxisome proliferator-activated receptor gamma via activation of p70 ribosomal protein S6 kinase. Blockage of the mTOR pathway by rapamycin treatment ameliorates alcohol-induced osteopenia by rescuing impaired osteo/adipogenic lineage differentiation of BMMSCs. In this study, we identify a previously unknown mechanism by which alcohol impairs BMMSC lineage differentiation and reveal a potential rapamycin-based drug therapy for alcohol-induced osteoporosis. Stem Cells 2016;34:2157-2168.

Reactive Oxygen Species Differentially Regulate Bone Turnover in an Age-Specific Manner in Catalase Transgenic Female Mice

Chronic ethyl alcohol (EtOH) consumption results in reactive oxygen species (ROS) generation in bone and osteopenia due to increased bone resorption and reduced bone formation. In this study, transgenic C57Bl/6J mice overexpressing human catalase (TgCAT) were used to test whether limiting excess hydrogen peroxide would protect against EtOH-mediated bone loss. Micro-computed tomography analysis of the skeletons of 6-week-old female chow-fed TgCAT mice revealed a high bone mass phenotype with increased cortical bone area and thickness as well as significantly increased trabecular bone volume (P < 0.05). Six-week-old wild-type (WT) and TgCAT female mice were chow fed or pair fed (PF) liquid diets with or without EtOH, approximately 30% of calories, for 8 weeks. Pair feeding of WT had no demonstrable effect on the skeleton; however, EtOH feeding of WT mice significantly reduced cortical and trabecular bone parameters along with bone strength compared with PF controls (P < 0.05). In contrast, EtOH feeding of TgCAT mice had no effect on trabecular bone compared with PF controls. At 14 weeks of age, there was significantly less trabecular bone and cortical cross-sectional area in TgCAT mice than WT mice (P < 0.05), suggesting impaired normal bone accrual with age. TgCAT mice expressed less collagen1α and higher sclerostin mRNA (P < 0.05), suggesting decreased bone formation in TgCAT mice. In conclusion, catalase overexpression resulted in greater bone mass than in WT mice at 6 weeks and lower bone mass at 14 weeks. EtOH feeding induced significant reductions in bone architecture and strength in WT mice, but TgCAT mice were partially protected. These data implicate ROS signaling in the regulation of bone turnover in an age-dependent manner, and indicate that excess hydrogen peroxide generation contributes to alcohol-induced osteopenia.

Alcohol: A Simple Nutrient with Complex Actions on Bone in the Adult Skeleton

BACKGROUND

Alcohol is an important nonessential component of diet, but the overall impact of drinking on bone health, especially at moderate levels, is not well understood. Bone health is important because fractures greatly reduce quality of life and are a major cause of morbidity and mortality in the elderly. Regular alcohol consumption is most common following skeletal maturity, emphasizing the importance of understanding the skeletal consequences of drinking in adults.

METHODS

This review focuses on describing the complex effects of alcohol on the adult skeleton. Studies assessing the effects of alcohol on bone in adult humans as well as skeletally mature animal models published since the year 2000 are emphasized.

RESULTS

Light to moderate alcohol consumption is generally reported to be beneficial, resulting in higher bone mineral density (BMD) and reduced age-related bone loss, whereas heavy alcohol consumption is generally associated with decreased BMD, impaired bone quality, and increased fracture risk. Bone remodeling is the principal mechanism for maintaining a healthy skeleton in adults and dysfunction in bone remodeling can lead to bone loss and/or decreased bone quality. Light to moderate alcohol may exert beneficial effects in older individuals by slowing the rate of bone remodeling, but the impact of light to moderate alcohol on bone remodeling in younger individuals is less certain. The specific effects of alcohol on bone remodeling in heavy drinkers are even less certain because the effects are often obscured by unhealthy lifestyle choices, alcohol-associated disease, and altered endocrine signaling.

CONCLUSIONS

Although there have been advances in understanding the complex actions of alcohol on bone, much remains to be determined. Limited evidence implicates age, skeletal site evaluated, duration, and pattern of drinking as important variables. Few studies systematically evaluating the impact of these factors have been conducted and should be made a priority for future research. In addition, studies performed in skeletally mature animals have potential to reveal mechanistic insights into the precise actions of alcohol and associated comorbidity factors on bone remodeling.

Signal transducer and activator of transcription 3 regulates CCAAT-enhancer-binding homologous protein expression in osteoblasts through upregulation of microRNA-205

The transcription factor, CCAAT-enhancer-binding protein homologous protein (CHOP), is induced by endoplasmic reticulum-stress and mediates programmed cell death. In osteoblasts, CHOP overexpression increases the rate of apoptosis, leading to osteoblastic dysfunction. However, the regulatory mechanisms underlying CHOP expression remain unclear. In the present study, western blot analysis was used to demonstrate that the activation of signal transducer and activator of transcription 3 (STAT3) inhibited the levels of the CHOP protein, whereas small interfering RNA-mediated the knockdown of STAT3 upregulated CHOP expression. Furthermore, STAT3 was shown to increase the expression level of microRNA (miR)-205. A luciferase reporter assay revealed that miR-205 was able to directly target the 3'-untranslated region of the CHOP gene to inhibit its protein expression. The miR-205 antisense largely abolished the inhibitory effect of STAT3 activation on the levels of CHOP protein. Therefore, the results demonstrated a previously unknown STAT3/miR-205/CHOP signaling pathway in osteoblasts, which may aid the understanding of the pathogenic mechanisms of associated diseases, including osteoporosis.

p47phox-Nox2-dependent ROS Signaling Inhibits Early Bone Development in Mice but Protects against Skeletal Aging

Bone remodeling is age-dependently regulated and changes dramatically during the course of development. Progressive accumulation of reactive oxygen species (ROS) has been suspected to be the leading cause of many inflammatory and degenerative diseases, as well as an important factor underlying many effects of aging. In contrast, how reduced ROS signaling regulates inflammation and remodeling in bone remains unknown. Here, we utilized a p47(phox) knock-out mouse model, in which an essential cytosolic co-activator of Nox2 is lost, to characterize bone metabolism at 6 weeks and 2 years of age. Compared with their age-matched wild type controls, loss of Nox2 function in p47(phox-/-) mice resulted in age-related switch of bone mass and strength. Differences in bone mass were associated with increased bone formation in 6-week-old p47(phox-/-) mice but decreased in 2-year-old p47(phox-/-) mice. Despite decreases in ROS generation in bone marrow cells and p47(phox)-Nox2 signaling in osteoblastic cells, 2-year-old p47(phox-/-) mice showed increased senescence-associated secretory phenotype in bone compared with their wild type controls. These in vivo findings were mechanistically recapitulated in ex vivo cell culture of primary fetal calvarial cells from p47(phox-/-) mice. These cells showed accelerated cell senescence pathway accompanied by increased inflammation. These data indicate that the observed age-related switch of bone mass in p47(phox)-deficient mice occurs through an increased inflammatory milieu in bone and that p47(phox)-Nox2-dependent physiological ROS signaling suppresses inflammation in aging.

A look behind the scenes: the risk and pathogenesis of primary osteoporosis

Osteoporosis is a common disorder, affecting hundreds of millions of people worldwide, and characterized by decreased bone mineral density and increased fracture risk. Known nonheritable risk factors for primary osteoporosis include advanced age, sex-steroid deficiency and increased oxidative stress. Age is a nonmodifiable risk factor, but the influence of a person's lifestyle (diet and physical activity) on their bone structure and density is modifiable to some extent. Heritable factors influencing bone fragility can be monogenic or polygenic. Osteogenesis imperfecta, juvenile osteoporosis and syndromes of decreased bone density are discussed as examples of monogenic disorders associated with bone fragility. So far, the factors associated with polygenic osteoporosis have been investigated mainly in genome-wide association studies. However, epigenetic mechanisms also contribute to the heritability of polygenic osteoporosis. Identification of these heritable and nonheritable risk factors has already led to the discovery of therapeutic targets for osteoporosis, which emphasizes the importance of research into the pathogenetic mechanisms of osteoporosis. Accordingly, this article discusses the many heritable and nonheritable factors that contribute to the pathogenesis of primary osteoporosis. Although osteoporosis can also develop secondary to many other diseases or their treatment, a discussion of the factors that contribute only to secondary osteoporosis is beyond the scope of this Review.

NADPH oxidases in bone homeostasis and osteoporosis

Bone formation and degradation are perfectly coordinated. In case of an imbalance of these processes diseases occur associated with exaggerated formation of new bone or bone loss as in osteoporosis. Most studies investigating osteoporosis either focus on osteoblast or osteoclast function and differentiation. Both processes have been suggested to be affected by reactive oxygen species (ROS). Besides a potentially harmful role of ROS, these small molecules are important second messengers. The family of NADPH oxidases produces ROS in a controlled and targeted manner, to specifically regulate signal transduction. This review will highlight the role of reactive oxygen species in bone cell differentiation and bone-loss associated disease with a special focus on osteoporosis and NADPH oxidases as specialized sources of ROS.

Phosphate enhances reactive oxygen species production and suppresses osteoblastic differentiation

Phosphate has been shown to work as a signaling molecule in several cells including endothelial cells and chondrocytes. However, it is largely unknown how phosphate affects osteoblastic cells. In the present study, we investigated the effects of phosphate on reactive oxygen species (ROS) production and osteoblastic differentiation in murine osteoblastic MC3T3-E1 cells. Phosphate increased production of ROS in MC3T3-E1 cells and the inhibitors of sodium-phosphate cotransporter and NADPH oxidase suppressed ROS production by phosphate. Silencing Nox1 and Nox4 also inhibited the increase of ROS by phosphate. Phosphate also decreased alkaline phosphatase activity induced by bone morphogenetic protein 2 and this inhibition was abrogated by an inhibitor of NADPH oxidase. Furthermore, phosphate decreased the expression of osteoblastic marker genes in MC3T3-E1 cells. These results indicate that phosphate suppresses osteoblastic differentiation at least in part by enhancing ROS production in MC3T3-E1 cells.

Genistein supplementation increases bone turnover but does not prevent alcohol-induced bone loss in male mice

Chronic alcohol consumption results in bone loss through increased bone resorption and decreased bone formation. These effects can be reversed by estradiol (E2) supplementation. Soy diets are suggested to have protective effects on bone loss in men and women, as a result of the presence of soy protein-associated phytoestrogens such as genistein (GEN). In this study, male mice were pair-fed (PF), a control diet, an ethanol (EtOH) diet, or EtOH diet supplemented with 250 mg/kg of GEN for 8 weeks to test if GEN protects against bone loss associated with chronic drinking. Interestingly, alcohol consumption reduced cortical area and thickness and trabecular bone volume in both EtOH and EtOH/GEN groups when compared to the corresponding PF and PF/GEN controls, P < 0.05. However, in the trabecular bone compartment, we observed a significant increase in overall trabecular bone density in the PF/GEN group compared to the PF controls. Bone loss in the EtOH-treated mice was associated with the inhibition of osteoblastogenesis as indicated by decreased alkaline phosphatase staining in ex vivo bone marrow cultures, P < 0.05. GEN supplementation improved osteoblastogenesis in the EtOH/GEN cultures compared to the EtOH group, P < 0.05. Vertebral expression of bone-formation markers, osteocalcin, and runt-related transcription factor 2 (Runx2) was also significantly up-regulated in the PF/GEN and EtOH/GEN groups compared to the PF and EtOH-treated groups. GEN supplementation also increased the expression of receptor activator of nuclear factor κ-B ligand (RANKL) in the PF/GEN, an increase that persisted in the EtOH/GEN-treated animals (P < 0.05), and increased basal hydrogen peroxide production and RANKL mRNA expression in primary bone marrow cultures in vitro, P < 0.05. These findings suggest that GEN supplementation increases the overall bone remodeling and, in the context of chronic alcohol consumption, does not protect against the oxidative stress-associated EtOH-mediated bone resorption.

Alcohol and bone

Alcohol is widely consumed across the world in different cultural and social settings. Types of alcohol consumption differ between (a) light, only occasional consumption, (b) heavy chronic alcohol consumption, and (c) binge drinking as seen as a new pattern of alcohol consumption among teenagers and young adults. Heavy alcohol consumption is detrimental to many organs and tissues, including bones. Osteoporosis is regularly mentioned as a secondary consequence of alcoholism, and chronic alcohol abuse is established as an independent risk factor for osteoporosis. The review will present the different mechanisms and effects of alcohol intake on bone mass, bone metabolism, and bone strength, including alcoholism-related "life-style factors" such as malnutrition, lack of exercise, and hormonal changes as additional causative factors, which also contribute to the development of osteoporosis due to alcohol abuse.

Involvement of reactive oxygen species in osteoblastic differentiation of MC3T3-E1 cells accompanied by mitochondrial morphological dynamics

Bone remodeling is regulated by local factors that regulate bone-forming osteoblasts and bone-resorbing osteoclasts, in addition to hormonal activity. Recent studies have shown that reactive oxygen species (ROS) act as an intracellular signal mediator for osteoclast differentiation. However the role of ROS on osteoblast differentiation is poorly understood. Here, we investigated the impact of ROS on osteoblastic differentiation of MC3T3-E1 cells. Osteogenic induction resulted in notable enhancement of mineralization and expression of osteogenic marker gene alkaline phosphatase, which were accompanied by an increase in ROS production. Additionally, we found that mitochondrial morphology dynamically changed from tubular reticulum to fragmented structures during the differentiation, suggesting that mitochondrial morphological transition is a novel osteoblast differentiation index. The antioxidant N-acetyl cysteine prevented not only ROS production but also mineralization and mitochondrial fragmentation. It is therefore suggested that the ROS-dependent signaling pathways play a role in osteoblast differentiation accompanied by mitochondrial morphological transition.

Loss of functional NADPH oxidase 2 protects against alcohol-induced bone resorption in female p47phox-/- mice

BACKGROUND

In bone, NADPH oxidase (NOX)-derived reactive oxygen species (ROS) superoxide and/or hydrogen peroxide are an important stimulus for osteoclast differentiation and activity. Previously, we have demonstrated that chronic ethanol (EtOH) consumption generates excess NOX-dependent ROS in osteoblasts, which functions to stimulate nuclear factor kappa-β receptor ligand (RANKL)-RANK signaling, thus increasing osteoclastogenesis and activity. This activity can be blocked by co-administration of EtOH with the pan-NOX inhibitor diphenylene idonium (DPI).

METHODS

To test whether EtOH-induced bone loss is dependent on a functional NOX2 enzyme, 6-week-old female C57BL/6J-Ncf1/p47phox(-/-) (p47phox KO) and wild-type (WT) mice were pair-fed EtOH diets for 40 days. Bone loss was assessed by 3-point bending, micro-computed tomography and static histomorphometric analysis. Additionally, ST2 cultured cells were co-treated with EtOH and NOX inhibitors, DPI, gliotoxin, and plumbagin, after which changes in ROS production, and in RANKL and NOX mRNA expression were analyzed.

RESULTS

In WT mice, EtOH treatment significantly reduced bone density and mechanical strength, and increased total osteoclast number and activity. In EtOH-treated p47phox KO mice, bone density and mechanical strength were completely preserved. EtOH p47phox KO mice had no changes in osteoclast numbers or activity, and no elevations in serum CTX or RANKL gene expression (p < 0.05). In both WT and p47phox KO mice, EtOH feeding reduced biochemical markers of bone formation (p < 0.05). In vitro EtOH exposure of ST2 cells increased ROS, which was blocked by pretreating with DPI or the NOX2 inhibitor gliotoxin. EtOH-induced RANKL and NOX2 gene expression were inhibited by the NOX4-specific inhibitor plumbagin.

CONCLUSIONS

These data suggest that NOX2-derived ROS is necessary for EtOH-induced bone resorption. In osteoblasts, NOX2 and NOX4 appear to work in tandem to increase RANKL expression, whereas EtOH-mediated inhibition of bone formation occurs via a NOX2-independent mechanism.

Flavonoid intake and bone health

Flavonoids, found in a wide diversity of plant foods from fruits and vegetables, herbs and spices, essential oils, and beverages, have the most potential of dietary components for promotion of bone health beyond calcium and vitamin D. Recent epidemiological studies show flavonoid consumption to have a stronger association with bone than general fruit and vegetable consumption. Bioactive flavonoids are being assessed for properties beyond their chemical antioxidant capacity, including anti-inflammatory actions. Some have been reported to enhance bone formation and to inhibit bone resorption through their action on cell signaling pathways that influence osteoblast and osteoclast differentiation. Future research is needed to determine which of the flavonoids and their metabolites are most effective and at what dose, as well as the mechanism of modulating cellular events, in order to set priorities for clinical trials.

Vitamin D supplementation protects against bone loss associated with chronic alcohol administration in female mice

Chronic alcohol abuse results in decreased bone mineral density (BMD), which can lead to increased fracture risk. In contrast, low levels of alcohol have been associated with increased BMD in epidemiological studies. Alcohol's toxic skeletal effects have been suggested to involve impaired vitamin D/calcium homeostasis. Therefore, dietary vitamin D supplementation may be beneficial in reducing bone loss associated with chronic alcohol consumption. Six-week-old female C57BL/6J mice were pair-fed ethanol (EtOH)-containing liquid diets (10 or 36% total calories) for 78 days. EtOH exposure at 10% calories had no effects on any measured bone or serum parameter. EtOH consumption at 36% of calories reduced BMD and bone strength (P<0.05), decreased osteoblastogenesis, increased osteoclastogenesis, suppressed 1,25-hydroxyvitamin D3 [1,25(OH)2D3] serum concentrations (P<0.05), and increased apoptosis in bone cells compared with pair-fed controls. In a second study, female mice were pair-fed 30% EtOH diets with or without dietary supplementation with vitamin D3 (cholecalciferol; VitD) for 40 days. VitD supplementation in the EtOH diet protected against cortical bone loss, normalized alcohol-induced hypocalcaemia, and suppressed EtOH-induced expression of receptor of nuclear factor-κB ligand mRNA in bone. In vitro, pretreatment of 1,25(OH)2D3 in osteoblastic cells inhibited EtOH-induced apoptosis. In EtOH/VitD mice circulating 1,25(OH)2D3 was lower compared with mice receiving EtOH alone (P<0.05), suggesting increased sensitivity to feedback control of VitD metabolism in the kidney. These findings suggest dietary VitD supplementation may prevent skeletal toxicity in chronic drinkers by normalizing calcium homeostasis, preventing apoptosis, and suppressing EtOH-induced increases in bone resorption.

Ormeloxifene inhibits osteoclast differentiation in parallel to downregulating RANKL-induced ROS generation and suppressing the activation of ERK and JNK in murine RAW264.7 cells

Ormeloxifene (Orm), a triphenylethylene compound, has been established as a selective estrogen receptor modulator (SERM) that suppresses the ovariectomy-induced bone resorption in rats. However, the precise mechanism underlying the bone-preserving action of Orm remains unclear. In this study, we evaluated the effect of Orm on osteoclast formation induced by receptor activator of nuclear factor κB ligand (RANKL) in the murine macrophage cell line RAW264.7. We also explored the mechanism of action of Orm by studying the RANKL-induced signaling pathways required for osteoclast differentiation. We found that Orm inhibited osteoclast formation from murine macrophage RAW264.7 cells induced by RANKL in a dose-dependent manner. Orm was able to abolish RANKL-induced reactive oxygen species (ROS) elevation and inhibited the transcriptional activation of two key RANKL-induced transcription factors namely activator protein-1 (AP-1) and NF-κB through mechanisms involving MAPKs. Activation of two MAPKs, i.e. ERK (MAPK1) and JNK (MAPK8), was alleviated by Orm effectively, which subsequently affected the activation of c-Jun and c-Fos, which are the essential components of the AP-1 transcription complex. Taken together, our results demonstrate that Orm potentially inhibits osteoclastogenesis by inhibiting ROS generation and thereby suppressing the activation of ERK1/2 (MAPK3/MAPK1) and JNK (MAPK8) and transcription factors (NF-κB and AP-1), which subsequently affect the regulation of osteoclastogenesis. These results provide a possible mechanism of action of Orm in regulating osteoclastogenesis, thereby supporting the beneficial bone-protective effects of this compound.

Curculigoside isolated from Curculigo orchioides prevents hydrogen peroxide-induced dysfunction and oxidative damage in calvarial osteoblasts

Reactive oxygen species (ROS), including H(2)O(2), play a critical role in the pathophysiology of osteoporosis. Therefore, agents or antioxidants that can inhibit ROS production have a high clinical value in the treatment of osteoporosis. Curculigoside (CUR), one of the main bioactive phenolic compounds isolated from the rhizome of Curculigo orchioides Gaertn., is reported to have potent antioxidant and anti-osteoporotic properties. However, there is no direct evidence to link the antioxidant capacity of CUR with the observed anti-osteoporotic effect, and relevant molecular mechanisms remain unclear. Therefore, we investigated the protective effects of CUR against oxidative stress in calvarial osteoblasts and discussed the related mechanisms. It was found that osteoblast viability decreased significantly after 48-h exposure to 400 μM of H(2)O(2), compared with vehicle-treated cells, and the cytotoxic effect of H(2)O(2) was reversed significantly when pretreated with 0.1-10 μM of CUR (P< 0.05). Pretreatment with 0.1-10 μM of CUR decreased ROS production and lipid peroxidation, and increased the activities of antioxidant enzymes, such as superoxide dismutase and glutathione peroxidase in osteoblasts induced by H(2)O(2). In addition, H(2)O(2)-induced reduction of differentiation markers such as alkaline phosphatase, calcium deposition, and Runx2 level was significantly recovered in the presence of CUR. CUR also reversed H(2)O(2)-induced stimulation of extracellular signal-regulated kinase 1/2, and nuclear factor-κB signaling and the inhibition of p38 mitogen-activated protein kinase activation. These results provide new insights into the osteoblast-protective mechanisms of CUR through reducing the production of ROS, suggesting that CUR may be developed as a bio-safe agent for the prevention and treatment of osteoporosis and other bone-related human diseases.

Alcohol and bone: review of dose effects and mechanisms

Alcohol is widely consumed across the world. It is consumed in both social and cultural settings. Until recently, two types of alcohol consumption were recognized: heavy chronic alcohol consumption or light consumption. Today, there is a new pattern of consumption among teenagers and young adults namely: binge drinking. Heavy alcohol consumption is detrimental to many organs and tissues, including bones, and is known to induce secondary osteoporosis. Some studies, however, have reported benefits from light alcohol consumption on bone parameters. To date, little is known regarding the effects of binge drinking on bone health. Here, we review the effects of three different means of alcohol consumption: light, heavy, and binge drinking. We also review the detailed literature on the different mechanisms by which alcohol intake may decrease bone mass and strength. The effects of alcohol on bone are thought to be both direct and indirect. The decrease in bone mass and strength following alcohol consumption is mainly due to a bone remodeling imbalance, with a predominant decrease in bone formation. Recent studies, however, have reported new mechanisms by which alcohol may act on bone remodeling, including osteocyte apoptosis, oxidative stress, and Wnt signalling pathway modulation. The roles of reduced total fat mass, increased lipid content in bone marrow, and a hypoleptinemia are also discussed.

The Protective Effect of Quercetin-3-O-β-D-Glucuronopyranoside on Ethanol-induced Damage in Cultured Feline Esophageal Epithelial Cells

Quercetin-3-O-β-D-glucuronopyranoside (QGC) is a flavonoid glucoside extracted from Rumex Aquaticus Herba. We aimed to explore its protective effect against ethanol-induced cell damage and the mechanism involved in the effect in feline esophageal epithelial cells (EEC). Cell viability was tested and 2',7'-dichlorofluorescin diacetate assay was used to detect intracellular H₂O₂ production. Western blotting analysis was performed to investigate MAPK activation and interleukin 6 (IL-6) expression. Exposure of cells to 10% ethanol time-dependently decreased cell viability. Notably, exposure to ethanol for 30 min decreased cell viability to 43.4%. When cells were incubated with 50 µM QGC for 12 h prior to and during ethanol treatment, cell viability was increased to 65%. QGC also inhibited the H₂O₂ production and activation of ERK 1/2 induced by ethanol. Pretreatment of cells with the NADPH oxidase inhibitor, diphenylene iodonium, also inhibited the ethanol-induced ERK 1/2 activation. Treatment of cells with ethanol for 30 or 60 min in the absence or presence of QGC exhibited no changes in the IL-6 expression or release compared to control. Taken together, the data indicate that the cytoprotective effect of QGC against ethanol-induced cell damage may involve inhibition of ROS generation and downstream activation of the ERK 1/2 in feline EEC.

Protection against osteoporosis by statins is linked to a reduction of oxidative stress and restoration of nitric oxide formation in aged and ovariectomized rats

Statins, 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors, have been used as a cholesterol-lowering drug to treat hyperlipidemia clinically. In recent years, accumulating evidence indicates the possible beneficial effect of statins on osteoporosis. The aim of present study was to investigate whether protection against osteoporosis by statins is linked to a reduction of oxidative stress and restoration of nitric oxide (NO) formation in aged and ovariectomized rats. The aged and ovariectomized rats were used as two models of osteoporosis for evaluation of the effect of simvastatin. It was found that simvastatin abated oxidative stress, increased NO production, subsequently attenuating osteoporosis in two models. In the in vitro studies, the protective effects against H(2)O(2)-induced cell injury were examined in the MG-63 human osteoblastic cells. It was found that simvastatin ameliorated H(2)O(2)-induced cell loss and cell apoptosis and increased alkaline phosphatase (ALP) activity in osteoblastic cells. Simvastatin abated oxidative stress through enhancing catalase, heme oxygenase 1 (HO-1), and superoxide dismutase (SOD) activity and suppressing NADPH oxidase activity. In addition, simvastatin raised nitric oxide synthase (NOS) activity and eNOS expression at basal condition; inhibited NOS activity and iNOS expression when treated with H(2)O(2). In conclusion, protection against osteoporosis by statins is linked to a reduction of oxidative stress and restoration of NO formation in aged and ovariectomized rats.